The present invention relates in general to footwear structures and, more particularly, it relates to footwear structures having an interlock between an outsole and a midsole and improvements to footwear structure components.
The ideal footwear design would incorporate the following essential features and characteristics: comfort, cushioning, shock absorption, stability, flexibility, support, good fit, and would also be lightweight. These features are achieved in, and are dependent upon, the structural and functional design elements of the footwear, which enhance the wearer""s ability to perform various activities without pain or inconvenience.
To date, prior art footwear constructions have failed to successfully combine the essential features of an ideal design. Prior attempts to create the ideal footwear design have been unsuccessful largely because prior structures have emphasized one of the above-noted features to the detriment of others. Furthermore, prior attempts to construct an ideal footwear design have failed to consider the importance of other key features such as industrialized construction, style and fashion.
Prior art footwear constructions that provide cushioning generally have three or four separate parts. First, such conventional footwear designs are provided with an outsole. The outsole is made of a durable material that extends across the lower surface of the shoe and contacts the ground during use to provide traction. The outsole may also have integrally molded full or partial sidewalls extending upwardly around its periphery. Second, a midsole is permanently joined to the outsole on its interior upper surface and any abutting outsole interior sidewall surfaces to provide a cushioning layer within the footwear structure. In some cases the midsole and outsole material are formed as one component of similar or dissimilar materials. Third, an upper, usually formed of leather, synthetics or other materials, is joined to the top surface of the midsole and any abutting interior sidewall surfaces of the outsole and midsole which extend upwardly around the periphery of the upper. Fourth, in many prior art constructions, a thin cushioning insole is further provided for disposal between the top surface of the midsole and the wearer""s foot.
The conventional footwear cushioning components and their positioning within the footwear structures of prior art constructions have several undesirable characteristics. For example, it is well known in the art that the cushioning properties of the materials used in footwear midsole and insole designs are substantially reduced after the footwear has been used for a period of time. In some instances, a substantial reduction in cushioning can occur in a relatively short period of time. The footwear midsole and insole components are typically made of various foam and rubber materials which are subjected to repeated application of impact forces and stress which cause compression set, degradation, and fatigue resulting in reduced resiliency and failed cushioning properties. The typical foam midsole and insole cushioning materials are various formulations of sheet stock or molded eva, polyethylene, and polyurethane. The typical rubber materials are latex and neoprene.
The midsoles in prior art footwear constructions have several undesirable characteristics. For example, the consumer at the point of purchase is unable to make an alternative choice in the cushioning characteristics of the midsole without selecting separate footwear designs. Also, the wearer is unable to replace the midsole component after it has degraded and lost its ability to provide adequate cushioning and support. In addition, the attachment of the midsole to other components in the footwear structure such as the top surface of the outsole, abutting outsole side wall interior surfaces, and to the formed upper negate the ability of the midsole component to adequately compress, deform, and rebound while providing maximum cushioning.
Another undesirable feature of prior art designs is that the ability of the footwear structure to provide maximum cushioning of the foot structures at the appropriate instant in the gait cycle is negated in prior footwear constructions by the positioning of semi-rigid and rigid structural elements in close proximity to the wearer""s foot. The semi-rigid and rigid structural elements are typically positioned below the wearer""s foot on the top surface of the midsole or slightly recessed into the top surface of the midsole. The typical semi-rigid and rigid structural elements are: shanks, shank stiffeners, lasting insoles, stabilizers, and fasteners. The shanks, shank stiffeners, lasting insoles, stabilizers, and fasteners are usually made of metals, fiber composites, thermoplastics, and fibrous paperboard. All of these semi-rigid and rigid structural elements negate the performance and cushioning ability of the midsole, and therefore negatively impact user comfort.
In some footwear constructions a lasting margin structure is formed by the combination of gathered upper materials and the adhesives used to attach the upper to the lasting insole or top surface of the midsole. This lasting margin structure extends around and projects inward from the periphery of the lasting insole or midsole to a distance of approximately 15.0 mm to 25.0 mm creating a semi-rigid border within the footwear structure. This formed structure also negates the performance and cushioning ability of the midsole, to the detriment of user comfort.
Furthermore, prior art midsoles have external surfaces, especially along the side portions thereof, which are exposed to environmental conditions such as heat, cold, water, ultraviolet rays, abrasion from rocks, sand, soil, punctures from sharp pointed objects, and cuts from sharp edged objects. The environmental conditions contribute to the failure of midsole component cushioning in two main ways: degradation of the midsole cushioning materials, and destruction of the means by which the midsole cushioning component is attached to the footwear structure. Another undesirable feature of prior art designs is that the thin cushioning insole which is positioned between the top surface of the lasting insole or midsole and the wearer""s foot is typically too thin to provide optimal cushioning.
In an attempt to overcome some of the above-described deficiencies of prior art designs, some prior art constructions have incorporated custom or removable midsole inserts. These structures, however, remain encumbered by undesirable characteristics. One such structure is described in U.S. Pat. No. 4,881,328 (hereinafter xe2x80x9cthe ""328 patentxe2x80x9d) to Lin Yung-Mao. The ""328 patent describes a structure with an outsole and a peripheral midsole. A midsole insert is disposed over the peripheral midsole with cushioning elements extending downward adjacent the outsole. Unfortunately, the midsole insert and cushion elements must conform to a matching lift height of the peripheral midsole member. The peripheral midsole member also provides the only method of retaining midsole insert and structural support for the peripheral area of the shoe. The upper must be attached to the top surface of the peripheral midsole member, and the bottom surface of the peripheral member is attached to the upper surface of the outsole. The midsole insert must have an outwardly projecting lip to cover the upper that is attached at the peripheral member. Thus, the method of construction is complex and inefficient, and does not provide for maximum full perimeter cushioning since the rigid peripheral member is in close proximity to the user""s foot. The structure also has no means of providing for a midsole insert for a raised heel design typically found in dress, casual shoe, and boot constructions, and fails to provide air circulation within the structure.
Thus, a need exists in the art for an improved footwear structure that provides full perimeter maximum cushioning of the foot structures, support and stability for the foot structures, allows the positioning of semi-rigid and rigid structural elements away from the wearer""s foot, and can provide maximum cushioning without the restrictions caused by attachment of the midsole to other components in the footwear structure. Further, a need exists for a removable or non-removable midsole that: can be selected according to the wearer""s cushioning preference, can be selected according to the wearer""s weight, can be selected according to various performance feature options, can provide air circulation within the footwear""s interior environment, can be replaced after a substantial reduction and degradation of midsole cushioning occurs and can protect the midsole cushioning element from damage due to environmental conditions. A need also exists for a structure that allows for manufacturing efficiencies by facilitating use of differently sized midsoles with a single upper construction.
The footwear structure of the present invention is organized about the concept of providing an outsole and/or an upper having a shank interlock portion which mates with a corresponding shank interlock portion in a separate midsole. In one embodiment, the outsole and/or upper has an upward extending arc (either a continuous arc or an abruptly changing arc) in the shank area which defines the shank interlock portion therein. The midsole has a corresponding arc that defines the shank interlock portion on a bottom surface thereof which mates with the shank interlock in the outsole and/or upper.
Advantageously, the midsole may be permanently secured in the structure, or it may be left unsecured within the structure to allow for removal and replacement. In the case where the cushionability of the midsole degrades over time, the midsole may be removed and replaced to restore the overall comfort of the shoe. In addition, a semi-rigid or rigid shank insert, or a stabilizing material, may be provided between the midsole and the outsole, thereby removing rigid structural components from close proximity to a user""s foot. Other advantageous features for providing air flow within the shoe, heel and forefoot cushioning, and manufacturability are also provided. For example, a stretch upper may be provided to allow use of a single upper with a variety of midsole configurations. Moreover, the midsole may be provided in multiple layers in embodiments that are useful with or without mating shank interlock areas.
In particular, a footwear structure according to one embodiment of the present invention includes a midsole, and an upper having a bottom portion positioned below the midsole. The bottom portion of the upper has a shank interlock portion interlocking with a corresponding shank interlock portion in the midsole. Interlocking of the shank interlock portions of the upper and the midsole resists motion of the midsole relative to the upper. The structure may also include an outsole with a shank interlock portion that mates with the shank interlock portions in the midsole and the upper, the bottom portion of the upper being disposed between the midsole and the outsole. The shank interlock portions may include a continuous arc or an abruptly changing arc.
The upper may be provided in a number of embodiments. The upper may be a molded upper integrally formed with the outsole, or may include a plurality of closure straps. The upper may also include a stretch zone that stretches to allow interlocking of the shank interlock portion of the upper with corresponding shank interlock portions of a plurality of differently sized ones of the midsoles. The upper may also include a removable bootie portion that is removable from a second portion, and the midsole may be disposed within the bootie. The upper may also include a molded receptacle, and a portion of the midsole may be disposed within the molded receptacle.
The midsole may be permanently affixed in the structure, or may be removable therefrom. The top surface of the midsole may be contoured to define a footbed generally conforming to the bottom of a person""s foot, and may include an upwardly extending perimeter wall. The midsole may include a plurality of layers, with at least a first one of the layers being less firm than a second one of the layers. In one embodiment, the firmness of the midsole layers may decrease from a top layer of the midsole to a bottom layer of the midsole. A shank component and/or reinforcing layer may be disposed between the midsole and the outsole, and may include a shank interlock portion that mates with the shank interlock portions of the midsole, the upper, and the outsole. In another embodiment, the upper may not be disposed between the midsole and the outsole, e.g. the upper may be disposed on top of the midsole. In this embodiment a shank component and/or reinforcing layer may be disposed between the upper and the midsole with shank interlock portions of the shank, midsole, and outsole, in mating relationship. The shank component may extend along the full length of the midsole or any portion thereof, and may include perimeter, cupping walls for stabilizing the midsole.
One method of forming a footwear structure consistent with the invention includes: providing a last including a foot volume portion and a midsole volume portion, and having a shank interlock area; placing an upper on the last; securing an outsole to the upper, the outsole having a shank interlock portion mating with a shank interlock portion in the upper; removing the last from the upper to thereby leave a cavity in the upper, the cavity including a foot volume portion and a midsole volume portion in the upper; and inserting a midsole in the midsole volume portion of the cavity, the midsole having a shank interlock portion mating with the shank interlock portion in the upper.